In recent years, extruded ceramic materials have been increasingly used as substrates for automotive catalytic converter products. During the course of there manufacture, these extruded ceramic substrates are forced through highly precise extrusion dies which are formed of ultra-hard materials.
The manufacture of extrusion dies from these ultra hard materials is an extremely precise process. The extrusion dies are formed with multiple apertures through which material to be extruded is forced under high pressure. In one method of forming the extrusion die, mechanical drills are used to provide the extrusion apertures. If the extrusion dies are formed of ultra-hard materials such as, for example, 17-4PH stainless steel or Inconel.RTM. 718 (a registered trademark of International Nickel Co., Inc.), the drilling rate used for aperture formation is very slow and a great deal of time and effort is expended in extrusion die formation. If softer die materials are used, the drilling rate is increased, but the life span of the resulting extrusion die is correspondingly shorter.
Because of these difficulties, apertures are now formed in extrusion dies by electrochemical machining techniques rather than by mechanical drilling. With an electrochemical machining process, the workpiece from which the die is to be formed is situated in a horizontally indexable but vertically fixed position relative to a vertically moveable drilling rig manifold. The manifold supports a plurality of drilling tubes, each of which is utilized to form an aperture in the workpiece. The drilling tubes operate as cathodes in the electrochemical machining process, while the workpiece comprises the anode. As the workpiece is flooded with an acid electrolyte from the drilling tubes, material is selectively deplated from the workpiece in the vicinity of the drilling tubes to form the requisite aperture pattern. U.S. Pat. No. 4,687,563 to Hayes, U.S. Pat. No. 5,320,721 to Peters, U.S. Pat. No. 5,322,599 to Peters, and European Patent Application, Publication No. 0245 545 to Peters disclose such processes. Although this production technique has found significant usefulness in the art, the resulting extrusion dies may have a variability in surface finish patterns across the die which can lead to extrusion problems such as bow or band. The present invention is directed to overcoming these deficiencies.